Pressure responsive electrical instrument



Dec. 12, 1961 M. E. BOURNS 3,013,236

PRESSURE RESPONSIVE ELECTRICAL INSTRUMENT Original Filed June 14, 1956INVENTOR. MARLAA/ E. Boumvs United States Patent j 3,613,236. a PRESSUREBESPQNSTVE. ELECTRICAL v ,IN3TRUMENT Marian E. Born-us, 2482 CarltonPlace, Riverside, Calif. Continnatronof application Ser. "No. 591,370,June 14, 1956. This application Apr. 11, 1961?, Ser. No. 21,2544'Claims. ((1338-41) The present invention relatesto pressure responsiveelectrical instrument, and is a continuation of my pendmg application,Serial No. 591,370, filed June i4, 1956, now Patent No. 2,932,807,entitled Pressure Responsive Electrical Instruments.

More specifically, the present invention relates to differentialpressure transducers of the type embodying an electrical signal means,such asa variable resistor or potentiometer, for measuring fluidpressure against either a vacuum, atmospheric pressure, or a secondfluid pressure as the reference.

The primary object of the present invention is to provide a sensitivepressuretransducer which is relatively immune to the efiects, of shock,vibration, and acceleration. This is an important advantage, inasmuch aspressure transducers of this type arefrequently exposed to severeconditions of vibration and acceleration, while being called upon anddeliver accurate pressure response, free of vibration andaccelerationcrror.

Another object of the invention is to provide a pressure transducer ofthe type described, wherein the electrical output is not affected bytemperature changes.

Still a further object of the invention is to provide a differentialpressure responsive instrument which is simple and inexpensive tomanufacture, while at the same time rugged in construction and having anextremely sensitive and accurate response to fluid pressure conditions.

These and other objects and advantages of the present invention willbecome apparent to those skilled in the art upon consideration of thefollowing detailed description of the preferred embodiment thereof,reference being had to the accompanying drawing, which is a crosssectional view taken through an instrument embodying the principles ofthe invention.

in the drawing, the pressure transducer is designated in its entirety bythe reference numeral Ill, and includes a housing consisting of a base11 and cover 12. The base 11 is preferably formed of dielectric materialsuch as plastic, ceramic, or the like, and the cover 12 is a metal cupextending down over the edges of the base 11 and secured thereto byscrews 13. Screwed into tapped holes in the bottom of the base 11 aretwo threaded pipes 14 and 15, which are connected to sources of fiuiclpressure (not shown).

Mounted side by side within the housing and parallel to one another, aretwo thin-walled, pressure sensitive bellows 20 and 21, each of which issecured at one end thereof by a tubular bushing 22 to the base 11. Thetubular bushings 22 are secured within holes in the base 11, and thecentral bore of the bushing opens into the interior of its respectivebellows. The bottom end of the tubular bushing 22 opens into a shortpassageway 23 which connects into the associated pipe 14, 15, and thesaid pipes are thus connected to the interior of the bellows so thatfluid pressure can be admitted thereto.

The top ends of the bellows 20, 21 are movable up and down responsive tochanges in the pressure dilferential between the inside and outside ofthe bellows. Secured to the movable end of each of the bellows is anupwardly projecting stud 24, having a socket 25 in its upper end toreceive the shank 30 of one of two relatively movable parts comprisingthe electrical signal means 31.

3,913,236 Patented Dec. 12, 1961 Thesignal means 31 may take any desiredform, but in the illustrated embodimentis shown as a potentiometerconsisting of a resistance element 32. and wiper contact 33. Theresistance element 32 is mounted on the movable end of the bellows 21and is elongated in configuration, with its lengthwise dimension, orlongitudinal axis, extending parallel to the line of travel of the freeend of the bellows. The element 32 may take any desired form, but ishere shown as a wire-wound type of element, which issecured to a support34. The support 34 is carried at the top end of the shank 30, which ismounted on the movable end of the bellows 21.

The wiper contact 33 is mounted on the movable end of the bellows 20,and is secured thereto by a s'upport'35. The support 35 is mounted onthe top end of the shank 30, which is attached to the stud 24 on themovable end of bellows 20. The contact 33 is preferably formedofresilient sheet metal, and is in the form of a long slender finger witha flared root portion which isattached to the support 35. The contact 33projects laterally from the support 35 over the exposed surface of theresistance element 32. A narrow ridge 36 on the end of the contact 33wipes on the element 32 to make electrical contact therewith, and as themovable end of the bellows 29 travels up and down responsive to changesin pressure differential, the contact ridge 36 wipes on the element 32from one end thereof to the other..

Wires 40 and 41 connect the ends of the resistance element 32 toterminals 42 and 43, respectively; the said terminals extending throughholes in the cover 12 and being insulated therefrom by rubber grommets44. Contact member 33 is likewise connected by a wire 45 to a thirdterminal 46, which extends through a hole in the cover 12 and isinsulated therefrom by a rubber grommet 47.

The two bellows 20 and 21 are preferably substantially identical inconstruction, and have substantially the same spring constant. Thus, anyvibration or acceleration forces applied to the instrument cause theelement 32 and contact 33 to move up and down together in synchronism.The electrical signal means is thus substantially unaffected by theeffects of vibration or acceleration. Also, since both of the bellows2i? and 21 are exposed to the same temperature conditions, any change inthe position of the contact 33 due to thermal effects is counteracted bya corresponding change in the position of the resistance element. Theinstrument is thus relatively unaffected by temperature changes.

The operation of the present invention is believed to be more or lessclear from the foregoing description and the drawing. Fluid pressure maybe introduced into either of the bellows 20 or 21 through pipes 14 or15. The other bellows may be evacuated and sealed, or opened toatmospheric pressure, or filled with gas or fluid at any desiredpressure, depending upon the desired reference pressure. The movable endof the bellows into which fluid pressure is admitted rises or falls withchanges in the pressure dilierential between the inside and outside ofthe bellows. This causes the contact member 33 and element 32 to bedisplaced with respect to one another in the vertical direction, so thatthe contact 33 is shifted along the length of the element. in the usualmethod of operation, voltage is applied across the end of the resistanceelement 32, and the position of the wiper 33 along the length of theelement is accurately shown by the voltage across terminal 46 and eitherof the terminals 42 or 43.

If it is desired to measure the diiterence between two different fluidpressures, the two pressures may be admitted to the interiors of both ofthe bellows 20, 21, respectively, in which case, both the element 32 andcon tact 33 will be displaced in the vertical direction, and theresultant shift of the contact 33 along the length of the element 32will be a function of the diflerence in pressures.

While I have shown and described in considerable detail what I believeto be the preferred form of my invention, it will be understood by thoseskilled in the art that various changes may be made in the shape andarrangement of the several parts without departing from the broad scopeof the invention, as defined in the appended claims.

1 claim:

1. A differential pressure transducer comprising a housing, a pair ofpressure sensitive bellows mounted on said housing, each of said bellowsbeing independent of the other and having a free end movable in responseto changes in the pressure differential between the inside and outsideof said bellows, the free ends of said beilows moving in parallel paths,means for introducing two different fluid pressures from separate sotces into said bellows, electrical signal means comprisig a resistanceelement mounted on the movable end of one of said bellows, and a contactmember connected to the movable end of the other of said bellows, andterminal means electrically connected to said resistance element and tosaid contact member.

2. A differential pressure transducer as defined in claim 1, whereinsaid two pressure sensitive bellows are substantially identical to oneanother and have substantially the same spring constant.

3; A differential pressure transducer comprising a housing having abase, a pair of. pressure sensitive bellows disposed side by side andparallel to one another, each of said bellows being independent of theother and having a fixed end attached to said base and a free endmovable in response to changes in the pressure differential between theinside and outside of said bellows, said free ends of said bellowsmoving in parallel paths, means for introducing two different fluidpressures from separate sources into said bellows, an elongatedresistance element mounted on the free end of one of said bellows, thelongitudinal axis of said resistance element being parallel to the lineof travel of said free end of said one beliows, a resilient springcontact finger fixed to the free end of the other of said bellows andprojecting laterally therefrom, said contact finger extendingtranversely across said resistance element and wiping thereon, andterminal means electrically connected to said resistance element and tosaid contact finger.

4. A ditferential pressure transducer as defined in claim 3, whereinsaid two pressure sensitive bellows are substantially identical to oneanother and have substantially the same spring constant.

References Cited in the file of this patent UNITED STATES PATENTS1,398,792 Paulin Nov. 2?), 1921 2,542,717 Smith Feb. 20, 1951 2,622,177Klose Dec. 16, 1952 2,889,527 Statham June 2, 1959

